The invention pertains to a roof drill bit, as well as a roof drill bit body and a hard cutting insert for use in a roof drill bit, that has a typical use of drilling boreholes in mine roofs. More particularly, the invention pertains to a roof drill bit, as well as a roof drill bit body and a hard cutting insert for use in a roof drill bit, that exhibits an improvement in the performance of drilling boreholes in a roof bolting operation due to an improvement in drilling debris evacuation and hard cutting insert retention. The major components of the roof drill bit, i.e., the roof drill body and the hard cutting insert, facilitate these performance improvements. U.S. Pat. No. 5,200,967 to Monyak, U.S. Pat. No. 6,595,305 B1 to Dunn et al., U.S. Pat. No. 6,684,968 B2 to Bise et al., U.S. Pat. No. 6,915,867 B2 to Bise, U.S. Pat. No. 6,945,340 B2 to Bise et al., and U.S. Pat. No. 7,168,511 B2 to Woods et al. disclose exemplary roof drill bits. Each one of these patents is hereby incorporated by reference herein.
Expansion of an underground mine (e.g., a coal mine) requires digging a tunnel that initially has an unsupported roof. To provide support for the roof, an operator drills boreholes using a roof drill bit wherein the boreholes can extend from about two feet to twenty feet into the earth strata. The roof drill bit attaches to a drill steel, which connects to a rotary driver. The rotary driver powers the roof drill bit to drill the boreholes. The operator then affixes roof bolts within the boreholes and a roof support (e.g., a roof panel) connects to the roof bolts to support the roof of the underground mine.
As one can appreciate, the drilling operation generates drilling debris. It is important to remove this drilling debris from the vicinity of the borehole. One typical way to remove or evacuate drilling debris from the vicinity of the borehole is to exert a vacuum at dust ports in the roof drill bit body. Under the vacuum, drilling debris passes through the dust ports and through a bore of a hollow drill steel into a debris collector. The debris collector is away from the borehole.
Although earlier roof drill bits, which utilize a vacuum to evacuate drilling debris, operate in a satisfactory fashion, there remains a need to improve upon the operation of the roof drill bit. More specifically, there is need to need to provide an improved roof drill bit that exhibits an improvement in the evacuation of drilling debris.
Roof drill bits operate at high rotational speeds. For example, a typical rotational speed is 650 rpm (revolutions per minute). When operating at such speeds, typically the drilling debris does not directly enter the dust port, but travels about the circumference of the roof drill bit prior to entering a dust port. In other words, the drilling debris does not directly enter the dust port closest to the point of engagement generating the drilling debris. Instead, the drilling debris travels about the circumference of the roof drill bit body prior to entry into a dust port that is not the dust port closest to the point of engagement. Significant disadvantages result from the inability of earlier roof drill bits to evacuate drilling debris directly through the dust ports.
One such disadvantage is excessive abrasive wear on the surface of the drill bit body. The drilling debris exhibits abrasive characteristics so that as the roof drill bit rotates at high speeds, drilling debris between the earth strata defining the borehole and the roof drill bit body abrades the roof drill bit body. Such abrasion reduces the underlying support for the hard cutting insert, which over time may result in a premature removal of the roof drill bit from service, i.e., a reduction in the expected useful tool life. It would be highly desirable to provide an improved roof drill bit that provides for an improvement in the evacuation of drilling debris under the influence of the vacuum at the dust ports.
Another significant disadvantage associated with the inability of earlier roof drill bits to evacuate drilling debris directly through the dust ports is an increase in the tendency of the roof drill bit to become stuck once the roof drill bit ceases operation. The presence of drilling debris between the roof drill bit and the earth strata defining the borehole can make removal of the roof drill bit-drill steel assembly difficult. The drilling debris actually can frictionally hold or retain the roof drill bit within the borehole. Thus, upon cessation of the rotation of the roof drill bit, an attempt by the operator to remove the roof drill bit-drill steel assembly may encounter problems. For example, the operator may be unable to remove the entire roof drill bit-drill steel assembly without great difficulty. As another example, during an attempt to remove the roof drill bit-drill steel assembly from the borehole, the drill steel may disengage from the roof drill bit. The result is that the roof drill bit remains stuck in the borehole. As one can appreciate, these difficulties decrease the overall production efficiency of the mining operation. Thus, they would be highly desirable to provide an improved roof drill bit that better evacuates drilling debris so as to reduce or eliminate drilling debris retained between the earth strata defining the borehole and the roof drill bit.
Typically, a roof drill bit uses a cemented carbide hard insert, which is at the axial forward end of the roof drill bit body, to first impinge the substrate or earth strata. The hard insert is brazed within a slot at the axial forward end of the roof drill bit body so there is a braze joint between the roof drill bit body and the hard insert. Typically, an increase in braze joint area generally leads to an increase in the braze joint strength. Such an increase in braze joint strength facilitates better retention of the hard insert to the roof drill bit body. Better drilling efficiencies result from using a roof drill bit with better retention of the hard insert (or cutting member) thereto. Thus, it would be highly desirable to provide an improved roof drill bit with a braze joint between the hard insert and the roof drill bit body that exhibits a greater braze joint area than heretofore.
In a roof drill bit, the roof drill bit body provides support for the hard insert affixed thereto. Heretofore, the roof drill bit body has not provided full support for the hard insert affixed thereto. In other words, the roof drill bit body does not contact or support the entire bottom surface of the hard insert, but instead, the corners of the hard insert adjacent the cutting edges lack support by the roof drill bit body. The lack of such support can lead to the loss of the hard insert, which can equate to a premature failure of the roof drill bit. Thus, it would be highly desirable to provide an improved roof drill bit that provides full support to the hard insert affixed thereto.
The working environment of an underground mine has inherent dangers due to an unsupported roof. Thus, it is advantageous to be able to drill the boreholes in an efficient fashion to minimize the time the roof is without support. One can increase the overall efficiency of the drilling operation by providing a roof drill bit that better evacuates drilling debris through the dust ports thereof. One can increase the overall efficiency of the drilling operation by providing a roof drill bit that better retains the hard insert to the roof drill bit body during the drilling operation.